Sinking basement floors can be indications of a variety of basement problems. All of these problems are potentially serious ones, and serious attention should be paid attention to them, as they can indicate a very serious foundation problem. Below are the most common causes of sinking floors in a basement:
Sometimes the appearance of a sinking floor is more than it seems. If the foundation has been raised up by swelling and expanding soils, it may lift the home upwards, leaving a void underneath the foundation floor.
In many situations the contractor may suggest that foundation push piers are installed to raise the foundation upwards, with the gap underneath filled via mud jacking.
Mud Jacking: "Mud jacking" is done by drilling 2" holes through the concrete basement floor. A mixture of soil and cement grout is then pumped into the void, adding solid strata underneath the home. The holes are then filled with a fluid mix of soil/cement grout, returning the floor to normal. However, if the sinking floor is accompanied by cracks forming in the foundation walls, an uneven foundation settlement, or a tilting chimney, the foundation may be experiencing a damaging settlement problem. Click to read more about addressing foundation settlement.
Improperly Sized Footing Pads
When a home is built, pillars are built in the basement or crawl space that are designed to transfer the home's weight to the virgin soil below the home. If these are the wrong size, they can fail to provide the proper support and weight distribution. As these pillars sink into the floor, the floor can sink with it.
Many contactors will address this problem by jacking up the house, lifting it upwards, in order to repair these support beams. The floor around the supports would be jackhammered, and footing pads would be repoured. The house would then be restored to its original position, and the floor concrete would be repoured in that area. This process requires extensive training and experience and should never be attempted by anyone who is not a professional in foundation repair.
Soil Erosion under the Floor
There can be an enormous amount of water movement underneath a foundation, especially if a home is built in the way of an underground stream, on bedrock, on a high water table, or in the natural pathway of moving rainwater. Over time, this can wash away the strata underneath a foundation, leading to empty space underneath the foundation. The result is a concrete slab with no support underneath, leading to fatigue and sinking of the floor. A contractor will likely address this problem though a combination of foundation piers and mud jacking.